Pi-joint assemblies are beginning to be more prevalent as the choice for assembling two structural elements together, whether or not the structure is a static or dynamic structure, such as is a structure used on an airplane. More importantly, the pi-joint assembly provides a way by which structural components are connected together, especially when the material of each component of the pi-joint is either a composite-to-composite or a composite-to-metallic type of connection and would otherwise require excessive material waste to fashion a typical joint connection out of one of the parts. By utilizing the pi-joint to connect structural elements, the weight of the overall structure may be reduced and the structural strength in a particular application may be increased.
One such pi-joint assembly for an aircraft is shown in FIGS. 1A and 1B. The pi-joint assembly 10 is comprised of a web 14, a pi-member 12 and a skin 18. An adhesive 16 is then typically filled in the gap formed between the web 14 and the pi-member 12 in such a way as to secure the two members. Other pi-members may be joined to the other sides of the web 14 in order to complete a given structure, thereby allowing structures like a wing of an airplane to be formed by multiple pi-joint assemblies. However, a disadvantage of such joints is the complicated assembly procedures required in order to properly align the parts prior to applying the adhesive 16 to secure the web 14 to the pi-member 12.
One known process to align the parts is by utilizing holes located in the parts, whereby the parts are located and aligned during assembly. The holes are then drilled to size after the parts are assembled, which necessitates the requirement of subsequently disassembling the parts to remove drill lubricant, chips and other foreign matter introduced between the parts during the drilling process. The cleaned parts are then reassembled and fasteners are installed along the part to “hold” the parts in alignment with each other while the past or adhesive is injected into the parts and while it cures. The alignment process may include shims or wires that are positionally located along and between the parts in order to insure a minimum bond thickness. The minimum bond thickness is required in order to insure maximum attachment strength between the two parts. After the adhesive starts to set or has partially cured, the shims and wires are removed. The voids that are created by removal of the shims and wires are then filled with additional adhesive. The additional steps of locating, drilling, cleaning, reassembly, fastening, shimming, unfastening, unshimming, and filling voids as mentioned above are termed “waste” which may be a disadvantage because time and money are lost due to the additional albeit necessary steps for the present method of assembly. Therefore, there is a need to have an improved method of assembly that reduces or eliminates the current steps. Also, there is a need to have an improved assembly that reduces or eliminates some of the assembly steps, assembly cycle time or assembly costs. Moreover, it would be advantageous to develop parts that reduces the dependency on tooling during the assembly process, reduces variation for part-to-part indexing and improves product repeatability and consistency. Lastly, it would be advantages to eliminate the need for shims and/or wires to achieve the minimum bond thickness on a pi-joint and it would be advantages to eliminate or reduce some of the associated assembly steps required by the shimming.
Lean manufacturing concepts may identify a way to eliminate this “waste” or at least provides direction in creating a solution. Lean Technology is all about eliminating “waste”—wasted time, wasted materials, and wasted money. Lean Technology is built on two fundamental principles: (1) elimination of waste, (2) accelerating flow in the process. The attempt is to eliminate all activities that do not add to the value of the assembly or product. Once a process is understood, the product can be assembled typically faster and in a more direct and efficient way. Simplifying the design or standardizing assembly processes may accomplish this efficiency. Some Lean Technologies have experienced up to 95% reductions in cost, cycle time, and defects. Non-value added work is also identified as waste, because it is work that is unnecessary in achieving the requirements of a final product. Eliminating non-value added work is also of benefit in saving time or money.
It may also be beneficial to use snap joint technology in a novel and inventive way to solve or improve the uncertainty of locating and aligning pi-assembly members. Snap joint assemblies provide a robust way in which to couple multiple parts together, moreover a snap joint allows for a the precise placement and alignment of the parts. Therefore it may be desirable to utilize this technology in order to provide an improved method of pi-joint assembling.